An antenna mounted in a mobile electronic device used in an RFID system is disclosed in Japanese Unexamined Patent Application Publication No. 2002-325013 (Patent Document 1). FIG. 1 is a top view illustrating the structure of an antenna apparatus described in Patent Document 1.
An antenna coil 30 illustrated in FIG. 1 includes an air core coil 32 and a planar magnetic core member 33. The air core coil 32 is configured by spirally winding conductors 31 (31a, 31b, 31e, and 31d) in a plane on a film 32a. The magnetic core member 33 is inserted into the air core coil 32 so as to be substantially parallel to a plane of the air core coil 32. The air core coil 32 has an aperture 32d and the magnetic core member 33 is inserted into the aperture 32d. A first terminal 31a is connected to a connecting conductor 31e via a through hole 32b, and a second terminal 31b is connected to the connecting conductor 31e via a through hole 32c. And, the magnetic-material antenna is arranged on a conductive plate 34.
The rear face of the magnetic-material antenna in Patent Document 1 illustrated in FIG. 1 is a metal plate, and the magnetic flux flows laterally (from right to left in the state illustrate in FIG. 1). The flowing magnetic flux produces an electromotive force in the coil conductor to pass an electric current through the coil conductor.
However, the magnetic-material antenna in Patent Document 1 has a structure in which coupling with the magnetic flux that is parallel to the rear conductive plate 34 is achieved, as illustrated in FIG. 1. Accordingly, when the antenna is mounted in, for example, a mobile phone terminal, the mobile phone terminal cannot be used with being held over the surface of a reader-writer in parallel if the antenna is installed in parallel with a circuit board in the casing of the mobile phone terminal. In addition, when the antenna coil is placed near the center of the conductive plate 34, the communication is established only within a short range and the position where the maximum communication distance is achieved is greatly shifted from the center of the casing, thus degrading the usability.